AWS Lambda RequestHandler for a void output

Question

Consider a simple Lambda written in Java:

import com.amazonaws.services.lambda.runtime.Context; 
import com.amazonaws.services.lambda.runtime.RequestHandler;

public class Hello implements RequestHandler<Integer, String>{
    public String handleRequest(int myCount, Context context) {
        return String.valueOf(myCount);
    }
}

The handler interface is defined as RequestHandler<InputType, OutputType>, but when my Lambda reacts to events and just does some side effects, is the output type unnecessary and I have to write something like this:

public class Hello implements RequestHandler<SNSEvent, Void>{
    public Void handleRequest(SNSEvent snsEvent, Context context) {
        ...
        return null;
    }
}

Which is annoying.

Is there an alternative to RequestHandler for a void handler?:

public class Hello implements EventHandler<SNSEvent>{
    public void handleEvent(SNSEvent snsEvent, Context context) {
        ...
    }
}

Answer 1

You don't need to implement an interface for your Lambda entry point. Your handler class can just be a POJO with a signature that fulfils the requirements explained in the documentation.

For example:

package example;

import com.amazonaws.services.lambda.runtime.Context;
import com.amazonaws.services.lambda.runtime.events.SNSEvent;

public class Hello {
  public void handleEvent(SNSEvent event, Context context) {
    // Process the event
  }
}

In this case you should use example.Hello::handleEvent as the handler configuration.

See also this example from the official docs:

package example;

import com.amazonaws.services.lambda.runtime.Context; 
import com.amazonaws.services.lambda.runtime.LambdaLogger;

public class Hello {
    public String myHandler(int myCount, Context context) {
        LambdaLogger logger = context.getLogger();
        logger.log("received : " + myCount);
        return String.valueOf(myCount);
    }
}